Ophiuchus

Ophiuchus


Transit Date of principal star:
15 June


There is some disagreement over the origin of this constellation. Apparently it was once known as Asclepius, who was the Greek god of medicine. One such reference was made in the writings of Eudoxus, in the fourth century BC.
Eudoxus (c400-c347 BC) deserves to be better known. He may have been a member of Plato's Academy, and it is possible he was its head for some time.

Eudoxus was a prolific writer of scientific subjects, and thinkers such as Euclid incorporated much of his work into their own. He mapped out the constellations, and the result became the main star reference for hundreds of years. Among other feats, he divided the sky into degrees of longitude and latitude and devised a better calendar. He was also a well known geographer and mathematician, but it was his work on astronomy that he is principally remembered.

Later Greek stories arose about Carnabon, a king of the Getae, who killed a famous dragon, or even of Heracles, who (you might recall) killed Draco. Thus the story of the man and serpent came to represent a host of individuals, but most authorities now seem to opt for Asclepius, or Aesculapius, which is the Latin equivalent of the Greek god of medicine.

Son of Apollo and a nymph called Coronis, Asclepius was taught medicine by the centaur Chiron. (His mythology also arises from Thessaly, where the stories of the centaurs originated.)

Asclepius became the Argonauts' surgeon, sailing with them on the ship Argo, and he managed to bring back to life a number of people, including the son of King Minos of Crete.

It was after Asclepius tried to revive Orion, bitten by the scorpion, that Pluto began to complain. He argued to Zeus that if Asclepius had his way he would rob Pluto of the entire population of Hades. Zeus agreed; they couldn't permit men to be immortal. So he sent a thunderbolt to end Asclepius's life.

Zeus later put Asclepius in the heavens along with the Serpent. The serpent has long been a symbol for renewed life.

While the cult of Asclepius began in Thessaly, temples were built throughout Greece, especially near healing springs. Around 300 BC the cult arrived in Rome.

Ancient sculpture typically shows the god bare breasted, attired in a long flowing cloak, and holding a staff with a serpent coiled about it. This is perhaps the forerunner of the modern medical symbol of the caduceus.


The constellation Ophiuchus is thus found in the midst of the Serpens. The southern part of Ophiuchus dips into a very dense portion of the Milky Way, resulting in a great many deep sky objects.

The Bayer stars of Ophiuchus are fairly bright, five of which have a magnitude brighter than 3.0.

The brightest star, alpha Ophiuchi, is better known as Rasalhague, meaning "Head of the Snake Charmer". This is a rather close star, at 54 light years away, and a celestial neighbour of Ras Algethi (alpha Herculis), which lies to the WNW five degrees.

Ophiuchus has a half-dozen or so visual doubles, and even more star clusters. In fact Ophiuchus has more globular clusters than any other constellation.

The region encircling rho Ophiuchi is also of some interest. This area contains several dark clouds and nebulae that show the active formation of stars.


Double stars in Ophiuchus:

[NOTE: See the Binocular Section, below, for updated binary values]

Ophiuchus has one of the finest collections of double stars, including several close visual binaries.

Eta Ophiuchi is a close visual with an orbit of 88 years: 2.9, 3.4; presently the companion is at PA 247 and separation 0.6".

Lambda Ophiuchi is also a rapid binary. 4.2, 5.2; currently the PA is 27 and its separation is 1.5".

Xi Ophiuchi: 4.5, 9.0; PA 50, separation 3.7".

Rho Ophiuchi: 5.3, 6.0; PA 344, 3.1".

Tau Ophiuchi: 5.2, 5.9; with an orbit of 280 years. Presently the companion is at PA 282 and separation 1.7".

36 Ophiuchi is a binary with period of 548 years, of two equal stars: 5.1, 5.1; 148, 4.9".

70 Ophiuchi is another close binary with a period of 88.3 years. 4.2, 6.0. In 2000.0 the values are PA 149 and separation 3.7".

Struve 2276. This is a very beautiful fixed binary of two fairly faint stars: 7.0, 7.4; PA 257, separation 6.9".


Variable stars in Ophiuchus:

Kappa Ophiuchi is an irregular (Lb) variable that fluctuates betweem 4.1 and 5.0.

Chi Ophiuchi is a gamma Cas variable: 4.2-5.0.

U Ophiuchi is an Algol type (EA) variable: 5.84-6.6 every 1.7 days.

X Ophiuchi is a long-period variable, 5.9-9.2 with a period of 328.85 days. In the year 2000 the maximum should occur during the last week of March.


Deep Sky Objects in Ophiuchus:

There are six Messier objects in Ophiuchus: M9, M10, M12, M14, M19, and M62 (and one more as well, if you accept M107 as a true Messier). These are all globular clusters.

M9 (NGC 6333) is the smallest of this group, unresolved except in large instruments.

The cluster is found 3.5 degrees SE of eta Ophiuchi. It is considered to be about 26,000 light years away.

In the same field are two more globular clusters: NGC 6342 (1 degree SE) and NGC 6356 (1 degree NE).

M10 (NGC 6254) and M12 (NGC 6218) are nearly identical globular clusters: like tiny explosions of stars with dense cores.

M12 is eight degrees north of zeta Ophiuchi and two degrees east. M10 is 2.5 degrees SE of M12, with 30 Ophiuchi in the same field.
M14 (NGC 6402) needs a 20-cm telescope to resolve; it's more condensed than the preceding two and slightly fainter.

M19 (NGC 6273) is another very dense cluster, usually described as "oblate", meaning it's a bit egg-shaped. It is about 25000 light years away.

M19 is seven degrees due east of Antares (alpha Sco), or two and a half degrees west of the bright double 36 Ophiuchi (and very slightly north, less than a degree).
M62 (NGC 6266) is six degrees SW of theta Oph (and four degrees south of M19); this is another non-circular globular cluster, a little brighter than M19. (Note: Burnham includes this Messier in Scorpius; nearly all other authorities put it in Ophiuchus.)

M107 (NGC 6171) is the faintest of the bunch and quite small. This is one of those "Messiers" that were added to the original list, for some reason. It's three degrees SSW of zeta Ophiuchi.

B78, the "Pipe Nebula", is a naked eye dark nebula two degrees southeast of theta Ophiuchi, in very rich area of the Milky Way.

Barnard's Star is the most rapidly moving star relative to the solar system, with a proper motion of 10.31", and the second closest star to us, at a distance of 5.91 light years (if you accept the three-star system of alpha Centauri as a unit).

This is a red dwarf, with a visual magnitude of only 9.5, and consequently not easily found. Burnham has a finder's chart, page 1253, but since that chart was published the star has moved north 1.1 centimetres.

The star is three degrees due east of beta Ophiuchus. The actual location (Epoch 2000) is R.A. 17h58m; Decl. +04 degrees, 34 minutes.

A slight oscillation in both the right ascension and declination of Barnard's Star has led observers to suggest the possibility that one or more planets orbit the star.


For a more detailed appreciation of Ophiuchus, visit the Binocular Section.


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